(a) The Field of the Invention
The present invention relates in general to copolyester compositions for the production of fibers having high heat stability and resistance to the propagation of flame, to a process for making the same and to the copolyester textile fibers made from said compositions.
More particularly this invention refers to the production of copolyester fibers resistant to the propagation of flame, obtained from copolyester compositions containing, besides the normal components of polyethyleneterephthalate, a tetrabrominated diol and one or more oxides, preferably antimony or titanium oxide or borates of polyvalent metals, preferably zinc.
(B) The Prior Art
The technology for the production of spinnable copolyester compositions and of copolyester fibers which are flame resistant, more precisely resistant to the propagation of flame (that is for the production of so called "self-extinguishing" textile products) is known in the art and there is a patent literature concerning it (see e.g. U.S. Pat. No. 3,794,617 and German patent application publication No. 2,313,298).
To produce such copolyester fibers it is preferable to start from a spinnable copolyester composition including antiflame additives or combinations of such additives rather than to apply an antiflame finish to textile fibers or to finished textile products.
This second method has the well known disadvantage that the antiflame finish is progressively removed in use in the washings of the textile products.
Therefore the more recent technique for the production of antiflame textile products is oriented to the production of copolyester compositions which include one or more antiflame agents. It is known that by copolymerizing the normal components of polyethylene terephthalate with an halogenated, preferably a brominated or chlorinated, diol, flame resistance properties are enhanced. These diols are either chemically bound in the macromolecules or are added as additives. The association to a copolyester composition of the type indicated of antimony oxide, in particular Sb.sub.2 O.sub.3, which improves the self-extinguishing characteristics, is also known. According to what has been discussed in the art antimony oxide is added in amounts (in the order of 1% to 2% on the weight of the polyester) which are relatively low although they are clearly higher than those in which it would be used as a polycondensation catalyst. An antimony oxide, when not employed as a catalyst, is added to the solid polymer, which is normally in the form of chips or powder. This however has various drawbacks and in particular lowers the polymer molecular weight so much that it becomes unsuitable for the production of yarns.